This invention relates generally to coherent jet technology.
A recent significant advancement in the field of gas dynamics is the development of coherent jet technology which produces a laser-like jet of gas which can travel a long distance while still retaining substantially all of its initial velocity and with very little increase to its jet diameter. One very important commercial use of coherent jet technology is for the introduction of gas into liquid, such as molten metal, whereby the gas lance may be spaced a large distance from the surface of the liquid, enabling safer operation as well as more efficient operation because much more of the gas penetrates into the liquid than is possible with conventional practice where much of the gas deflects off the surface of the liquid and does not enter the liquid.
In a coherent gas jet system one or more gas jets are surrounded by a flame envelope or flame shroud to maintain coherency of the gas jet or jets over a long distance from the injection lance. The flame shroud is produced by combusting oxidant with gaseous fuel such as methane or natural gas. In some situations it may be desirable to use liquid fuel instead of gaseous fuel to generate the flame shroud. For example, liquid fuel may be preferred to gaseous fuel in areas where gaseous fuel is not regularly available on a consistent basis and/or in areas where the cost of gaseous fuel is high relative to liquid fuel. Unfortunately, the straightforward substitution of liquid fuel for gaseous fuel in a coherent gas jet system does not yield satisfactory results regarding the coherent jets.
Accordingly it is an object of this invention to provide a system for producing a coherent gas jet which can effectively employ liquid fuel to generate the requisite flame shroud.
The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:
A method for producing a coherent gas jet comprising:
(A) passing at least one gas jet from at least one nozzle into an injection volume, said nozzle(s) housed in a lance having a lance face and communicating with the injection volume at the lance face;
(B) passing liquid fuel into a recession on the lance face, said recession being around the nozzle(s);
(C) passing motive gas into the recession, creating a flow of liquid fuel within the recession, atomizing the liquid fuel, and passing atomized liquid fuel out from the recession into the injection volume annularly to the gas jet(s); and
(D) passing oxidant into the injection volume and combusting the oxidant with atomized liquid fuel to produce a flame shroud around the gas jet(s).
Another aspect of the invention is:
A coherent jet lance apparatus comprising:
(A) a lance having a lance face and having a least one nozzle having an opening at the lance face;
(B) a recession on the lance face around the nozzle opening(s);
(C) means for providing liquid fuel into the recession, and means for providing motive gas into the recession to atomize liquid fuel within the recession; and
(D) means for passing oxidant from the lance positioned radially outward of the recession.
As used herein the term xe2x80x9clance facexe2x80x9d means the surface of a lance abutting an injection volume.
As used herein the term xe2x80x9ccoherent jetxe2x80x9d means a gas jet which is formed by ejecting gas from a nozzle and which has a velocity and momentum profile along a length of at least 20d, where d is the exit diameter of the nozzle, which is similar to its velocity and momentum profile upon ejection from the nozzle. Another way of describing a coherent jet is a gas jet which has little or no change in its diameter for a distance of at least 20d.
As used herein the term xe2x80x9clengthxe2x80x9d when referring to a coherent gas jet means the distance from the nozzle from which the gas is ejected to the intended impact point of the coherent gas jet or to where the gas jet ceases to be coherent.